The use of semiconductor integrated circuit chips for data storage, such as portable flash memory cards, is widespread. Users of these devices desire ever-increasing data storage capacity, and manufacturers strive to provide a large storage capacity in a cost-effective manner, often while maintaining a standard package size to ensure compatibility with existing electronic devices.
It is known to achieve an increased memory density within a single package by stacking multiple semiconductor dice in a single package, known as a Multi-Chip Package (MCP). The increased number of dice provides a corresponding increase in storage capacity relative to a single die. Referring to FIG. 1, the MCP 100 consists of four NAND Flash memory dice 102. It should be understood that this method is equally applicable to other types of memory devices. Each die 102 has bonding pads 104 that are electrically connected via bond wires 106 to a common substrate 108. Although the dice 102 are shown with bonding pads 104 on two opposite sides, it should be understood that each die 102 may alternatively have a different arrangement of bonding pads 104, for example on a single side, or on two adjacent sides, or any other arrangement. The substrate 108 provides further electrical connections from the bond wires 106 to solder balls 110 on the opposite side of the substrate 108, forming a Ball Grid Array (BGA) for connection to an external device (not shown). An interposer 112 is provided between each pair of consecutive dice 102, to create a sufficient clearance therebetween to allow the attachment of the bond wires 106 to the bonding pads 104. This arrangement has the drawback that the thickness of the interposers 112 limits the number of dice 102 that can be stacked within a package of fixed dimensions, thereby limiting the total storage capacity of the MCP 100. In addition, because each die 102 overhangs the bonding pads 104 of the lower dice 102, the bond wires 106 for each die 102 must be attached prior to stacking the next die 102, resulting in an increased number of manufacturing steps and a time-consuming and labor-intensive assembly.
Another approach is shown in FIG. 2. The MCP 200 consists of four NAND Flash memory dice 202 with bonding pads 204 along one side. This arrangement may alternatively be used with dice 202 having bonding pads 204 along two adjacent sides, as will be discussed below in further detail. The dice 202 are laterally offset from one another to expose the bonding pads 204 of each die 202. In this arrangement, all of the dice 202 can be stacked in a single step, and thereafter all of the bond wires 206 can be attached in a single step by a wire bonding machine (not shown). This arrangement does not require interposers to provide access to the bonding pads 204, resulting in a more compact arrangement. This arrangement has the drawback that all of the bond wires 206 for all dice 202 must be attached along the same side(s) of the dice 202 and to the same surface of the substrate 208. The resulting high interconnect density may be congested and present logistic difficulties, particularly in devices such as HLNAND™ flash memory devices where each die 202 requires separate interconnect traces on the substrate 208. These can be addressed by providing additional interconnection layers on the substrate 208, which can increase the cost of manufacture.
Another approach is shown in FIG. 3. The MCP 300 consists of four NAND flash memory dice 302A, 302B, 302C, 302D in a staggered arrangement. The dice 302A, 302C have bonding pads 304 oriented along the left side, and the dice 302B, 302D have bonding pads 304 oriented along the right side. The lateral offset between consecutive dice 302 exposes the bonding pads 304, and the thickness of the dice 302 provides a sufficient clearance to attach the bond wires 306. For example, the die 302B provides a sufficient clearance between the dice 302A and 302C to attach bond wires 306 to the bonding pads 304 of the die 302A. The interconnect congestion of the substrate 308 is mitigated by the alternating orientation of the bonding pads 304, which allows half of the interconnections to be positioned on either side of the stack. However, this arrangement has the drawback that the bond wires 306 cannot all be attached in a single manufacturing step, because the dice 302C and 302D respectively overhang and block access to the bonding pads 304 of the dice 302A and 302B. In addition, the thickness of the dice 302B and 302C must provide a sufficient clearance to attach the bond wires 306 to the dice 302A and 302B, respectively. The clearance required is typically on the order of 100 microns. Although thinner dice 302 can be manufactured, they cannot be used without spacers in this arrangement to reduce the total height of the stack, thereby limiting the number of dice 302 that can be stacked in a package of fixed dimensions. As a result, the total storage capacity of the MCP 300 is limited and cannot be further improved by reducing the thickness of the dice 302.
Another approach is shown in FIG. 4. The MCP 400 consists of three NAND flash memory dice 402A, 402B, 402C, each with bonding pads 404 arranged on two opposite sides thereof. Each die 402 is sufficiently shorter in length than the die 402 immediately below it that it does not overlap the bonding pads 404 of the lower die 402. In this arrangement, all of the bonding pads 404 are accessible to attach the bond wires 406 in a single step for connection to the substrate 408. One drawback of this arrangement is that the dice 402 cannot all be made the same size, resulting in increased manufacturing complexity. In addition, dice of different dimensions do not have equal data storage capacity, requiring complex control circuitry.
At least some of the foregoing methods can be adapted to dice having bonding pads on two or more adjacent sides, for example by laterally offsetting the dice in two dimensions as shown in FIG. 5. However, these arrangements do not adequately address the above mentioned drawbacks, such as congestion of bonding wires and higher dice overhanging the bonding pads of lower dice.
Therefore, there is a need for a Multi-Chip Package having a high storage capacity.
There is also a need for a Multi-Chip Package having a low cost of manufacture.
There is also a need for a Multi-Chip Package having a compact arrangement.
There is also a need for a method of manufacturing a Multi-Chip Package in a reduced number of manufacturing steps.